The present invention relates to broadcast systems in general, and in particular to data broadcast systems, especially to systems providing Conditional Access services.
Systems for ensuring that, in a pay or subscription broadcast system, only those who have paid to receive broadcast content actually do receive the broadcast content are well-known in the art. Such systems, which often include many other features, are known as Conditional Access (CA) systems. Typically, pay broadcast systems generally broadcast encrypted material and utilize a CA system to deliver one or more appropriate decryption keys to authorized receivers only.
One CA system is described in U.S. Pat. Nos. 5,282,249 and 5,481,609, both to Cohen et al. The two Cohen et al. patents describe a scrambled television system. Scrambled television transmissions described in the Cohen et al. patents include both scrambled data representing television signals and coded control messages, also known in the art as ECMs. The ECMs of Cohen et al. include, in a coded form, data necessary for generating a control word (CW) which may be used to descramble the scrambled data representing television signals.
Data necessary for generating a control word is known in the prior art to take many different forms and may include, in general, at least any of the following: a control word; an encrypted control word which is intended to be decrypted before use; and a seed to a generating function such as, for example, a one-way function which generates the control word upon input of the seed. Throughout the present specification and claims the terms xe2x80x9ccontrol word generating informationxe2x80x9d and xe2x80x9cCW generating informationxe2x80x9d are used interchangeably to designate data necessary for generating a control word in any appropriate form, as described above.
While the two patents to Cohen et al. describe an analog system, that is, a system in which analog television data streams are broadcast to television sets, it is appreciated that similar ECM methods may also be used for digital television data streams, it being appreciated that scrambling methods appropriate to digital data would be used in digital television data streams.
The system of Cohen et al. and other systems described in the art share a feature of broadcasting an ECM synchronous to, generally immediately before or in a data stream parallel to, the actual scrambled broadcast. Typically, such an ECM is valid for a brief duration, with a new ECM being broadcast, in synchrony with a scrambled broadcast scrambled according to a new key, a few seconds, such as 10 seconds, after the broadcast of the previous ECM. Some systems have been described in which a key is sent, whether by broadcasting or by other means such as by mail, with a lower frequency, even once a month. Such a system is described, for example, in U.S. Pat. Nos. 4,484,027 and Re 33,189 to Lee et al.
Patents describing systems related to encrypted broadcasting and/or key distribution in encrypted broadcasting systems include the following:
U.S. Pat. No. 4,228,321 to Flanagan describes a privacy transmission system with remote key control, in which key control signals are produced at the unscrambling location and are both used for unscrambling at that location and also transmitted to a scrambling location for use in scrambling.
U.S. Pat. No. 4,531,020 to Wechselberger et al describes a method for controlling the simultaneous broadcast of enciphered digital information signals, for example in a radio or television broadcast environment, to a plurality of subscribers using several levels of enciphering keys.
U.S. Pat. No. 4,531,021 to Bluestein et al describes enciphering digital information for transmission using a first key, common to all receivers, and a second key specific to one receiver of a small group of receivers.
U.S. Pat. No. 4,864,615 to Bennett et al describes a system for reproduction of secure keys by using distributed key generation data and a distributed encrypted prekey.
U.S. Pat. No. 4,866,770 to Seth-Smith et al describes a system for distributing video, audio, teletext, and data, in which system wide, individual decoder and group decoder control signals are transmitted as part of a composite signal. The group decoder control signal includes information relating to a group of decoders, while the individual decoder control signal includes information relating to the operation of individual decoders.
U.S. Pat. No. 4,944,006 to Citta et al describes a secure data packet transmission system utilizing a global encryption key as well as address keys for encrypting individually addressed bit packets.
U.S. Pat. No. 5,301,247 to Rasmussen et al. describes a method for ensuring secure communications, in which two keys are combined together to produce a session key.
U.S. Pat. No. 5,499,298 to Narasimhalu et al describes a method for controlled dissemination of digital information, in which encrypted digital information is decrypted by a tamper-proof controlled information access device, which access being provided according to conditions specified by an information provider.
In general, methods of transmitting a scrambled digital signal, including ECMs, are well known. Some systems use a composite signal, that is, an analog or digital signal including a plurality of components. Typically the plurality of components includes both a scrambled television signal component and an ECM component, the ECM component comprising a plurality of ECMs. Prior art references which discuss examples of this type of signal include the following: DVB ETR289, xe2x80x9cDigital Video Broadcasting (DVB): Support for use of scrambling and conditional access (CA) within digital broadcasting systemsxe2x80x9d; and DVB SIM061, xe2x80x9cTechnical specification of DVB-Simulcryptxe2x80x9d, Apr. 1, 1997.
Other documents relating to broadcasting of digital information include the DVB Specification for Data Broadcasting, document SI-DAT 360 (TM 1779), Feb. 12, 1997; and ATSC Digital Television Standard, document A54, October 1995 and subsequent editions.
Other methods of transmitting a scrambled digital signal, particularly useful in a case where the signal includes sub-signals encoded according to various different methods, are described in xe2x80x9cCommon Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applicationsxe2x80x9d, DVB document A017, May 1996 and subsequent editions; and in xe2x80x9cCommon Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applicationsxe2x80x9d, CENELEC EN50221:1997.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
The present invention seeks to provide an improved method for delivering a control word or key relating to an item. The present method is particularly useful in cases where the item is relatively short in duration and is transmitted asynchronously relative to an ECM stream; that is, time synchronization of the item and an associated ECM in the ECM stream cannot be guaranteed, typically because of the short duration of the item. The present method is also particularly useful in cases where the number of items is very large, and it may be impractical to assign a separate ECM stream to each item.
Cases of the types referred to may occur particularly in a data broadcast network, where a defined data item, such as a computer program or a multimedia item, is broadcast to subscribers or customers who have subscribed to or are otherwise authorized to receive the item. An item of this type may be of relatively short duration, such as between a fraction of a second and a few seconds, and there may be a very large number of items,
Existing methods of sending an ECM stream synchronized with a data stream, such as a data stream comprising a television program, are inadequate to provide for control word or key delivery in the cases described above, since state of the art ECM delivery mechanisms are not able to provide synchronization to the sub-second level.
There is thus provided in accordance with a preferred embodiment of the present invention a key delivery method for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver, the method including transmitting an item entitlement control message (IECM) including item control information, transmitting a stream entitlement control message (SECM) including stream control information, and combining at least part of the item control information and at least part of the stream control information to produce the first item control word.
Further in accordance with a preferred embodiment of the present invention the transmitting-IECM step is performed before the transmitting-SECM step.
Still further in accordance with a preferred embodiment of the present invention the transmitting-IECM step is performed simultaneously with the transmitting-SECM step.
Additionally in accordance with a preferred embodiment of the present invention the method also includes utilizing the first item control word to decode the at least one encoded item.
Moreover in accordance with a preferred embodiment of the present invention the item control information includes an item key, and the stream control information includes a stream key, and the combining step includes computing the first item control word from the item key and the stream key.
Further in accordance with a preferred embodiment of the present invention the item control information includes a first seed, and the stream control information includes a second seed, and the combining step includes computing an item key from the first seed using an item key production function, computing a stream key from the second seed using a stream key production function, and computing the first item control word from the item key and the stream key.
Still further in accordance with a preferred embodiment of the present invention the step of computing an item key includes determining whether the receiver is authorized to compute the item key and computing the item key only if the receiver is authorized to compute the item key.
Additionally in accordance with a preferred embodiment of the present invention the step of computing a stream key includes determining whether the receiver is authorized to compute the stream key and computing the stream key only if the receiver is authorized to compute the stream key.
Moreover in accordance with a preferred embodiment of the present invention the at least one encoded item is transmitted asynchronously to the SECM.
Further in accordance with a preferred embodiment of the present invention the at least one encoded item includes a first plurality of encoded items.
Still further in accordance with a preferred embodiment of the present invention each of the first plurality of encoded items has a time duration, and the SECM includes a second plurality of SECMs transmitted with an average inter-SECM delay, and each of the first plurality of encoded items is associated with one of the second plurality of SECMs, and the time duration of at least one of the first plurality of encoded items is less than the average inter-SECM delay.
Additionally in accordance with a preferred embodiment of the present invention more than one of the first plurality of encoded items is associated with at least one of the second plurality of SECMs.
Moreover in accordance with a preferred embodiment of the present invention the first plurality of encoded items includes at least a first encoded item and a second encoded item, and the first encoded item and the second encoded item are transmitted substantially simultaneously.
Further in accordance with a preferred embodiment of the present invention the at least one encoded item includes a plurality of encoded items including a second item encoded with a second item control word, the method also including transmitting a second SECM including second stream control information, and combining the item control information and the second stream control information to produce the second item control word.
Still further in accordance with a preferred embodiment of the present invention the item control information includes item purchase information.
Additionally in accordance with a preferred embodiment of the present invention the first stream control information includes item purchase information.
Moreover in accordance with a preferred embodiment of the present invention the second stream control information includes item purchase information.
Further in accordance with a preferred embodiment of the present invention the item purchase information includes item price information.
Still further in accordance with a preferred embodiment of the present invention the item purchase information includes purchase access information and the method includes determining whether the receiver is entitled to purchase the first item based, at least in part, on the purchase access information.
Additionally in accordance with a preferred embodiment of the present invention the item purchase information includes access information and the method includes determining whether the receiver is entitled to access the first item based, at least in part, on the access information.
Moreover in accordance with a preferred embodiment of the present invention the first item is broadcast to a plurality of item receivers including the receiver.
Further in accordance with a preferred embodiment of the present invention the step of transmitting an IECM includes broadcasting the IECM.
Still further in accordance with a preferred embodiment of the present invention the step of transmitting an SECM includes broadcasting the SECM.
There is also provided in accordance with another preferred embodiment of the present invention a key production method for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver and in which an item entitlement control message (IECM) including item control information and a stream entitlement control message (SECM) including stream control information are also sent from the sender to the receiver, the method including extracting at least part of the item control information from the IECM and at least part of the stream control information from the SECM, and combining the at least part of the item control information and the at least part of the stream control information to produce the first item control word.
There is also provided in accordance with another preferred embodiment of the present invention a key delivery subsystem for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver, the key delivery subsystem including an item entitlement control message (IECM) production unit operative to produce an IECM including item control information, a stream entitlement control message (SECM) production unit operative to produce a SECM including stream control information, transmitting apparatus receiving the IECM from the IECM production unit and the SECM from the SECM production unit and operative to transmit the IECM and the SECM to the receiver, and combining apparatus located at the receiver for combining at least part of the item control information and at least part of the stream control information to produce the first item control word.
There is also provided in accordance with another preferred embodiment of the present invention a key production subsystem for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver and in which an item entitlement control message (IECM) including item control information and a stream entitlement control message (SECM) including stream control information are also sent from the sender to the receiver, the key production subsystem including a control information extractor for extracting at least part of the item control information from the IECM and at least part of the stream control information from the SECM, and control word production apparatus for combining the at least part of the item control information and the at least part of the stream control information to produce the first item control word.